"I finally got one to the hole," Potgieter said after missed opportunities on the green by three players led to the longest playoff of the season on the tour.
He celebrated on Sunday by embracing his caddie and shaking hands with Greyserman and his caddie before giving his father, Heinrich, a hug.
The 20-year-old Potgieter is the youngest player on the tour and its biggest hitter, averaging 326-plus yards off the tee. He became the ninth player to win for the first time this season.
Potgieter was born in South Africa, moved to Australia when he was eight and returned to South Africa at age 17 because the COVID-19 pandemic limited his opportunities to compete.
"We had to give up a lot, moving to Australia, moving back," he said.
"Emigrating is definitely not the easiest thing. Coming alone at the start of my career to the States and giving it a grind, and having my dad here has helped so much."
Potgieter won the British Amateur title at the age of 17 and became the youngest Korn Ferry Tour winner last year, paving the way for him to become the second-youngest player to earn a PGA Tour card through the minor league just after his 20th birthday. The youngest was Aussie Jason Day, who was 19 in 2007.
Chris Kirk was eliminated after missing a four-foot putt on the second playoff hole — that after pushing a nine-foot putt past the cup on the first extra hole with a chance to win.
Greyserman and Potgieter each had opportunities to win it on the 72nd hole at Detroit Golf Club, but couldn't convert birdie opportunities to break a tie at 22 under with Kirk.
"This one's going to sting for a little bit ... just wasn't my time," said Greyserman, who finished second for the fourth time after coming up short for his first PGA Tour victory.
Potgieter, two strokes ahead entering the round, closed with a three-under 69, and American duo Greyserman and Kirk each shot 67.
Michael Thorbjornsen (67) and Jake Knapp (68) finished a stroke out of the playoff.
Collin Morikawa, meanwhile, is still waiting to end his drought.
He shot a 68 to finish 19 under and in an eighth-place tie. The two-time major winner, who was the highest-ranked player in the field at world No.5, has not won the PGA Tour since October 2023.
Min Woo Lee (68) finished joint-13th at 18 under as the best-placed Australian and Harrison Endycott (72) five under.
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